Temperature sensors provide electronic devices with temperature measurements that can be used to signal overheating conditions and allow adjustments to be implemented before the overheating rises to damaging levels. Temperature sensors may also be used as components of industrial process control systems, environmental monitoring systems or in a wide variety of other applications. Temperature sensors may also be used during the development phase of an electronic device in order to measure heat buildup in the device. Based on the information provided by the temperature sensors, engineers can adjust the design of the device in order to maintain device temperatures within certain tolerances. In both production and development scenarios, the accuracy of the temperature sensor is crucial.
Certain temperature sensors may be integrated into a device being monitored by integrating certain components of the sensor within an integrated circuit of the device electronics. In these on-chip temperature sensors, temperature information may be collected by measuring the temperature of the die in which the sensor is integrated. Typically, the die temperature can be determined using sensors that are configured to measure a thermal voltage generated by a component integrated into the die, such as a diode or bipolar junction transistor. This thermal voltage output can then be used to calculate the temperature of the die.
The performance characteristics of temperature sensors that rely on thermal voltage measurements can vary significantly from device to device due to variances in the manufacturing process. In applications such as temperature sensors that require high accuracy and precision, each individual sensor may be adjusted (i.e., trimmed) in order to account for the manufacturing variances and confirm the operating characteristics of the sensor prior to deployment. Prior to trimming a temperature sensor, the accuracy of the sensor must first be determined. There are two principle mechanisms for measuring the accuracy of a temperature sensor.
The first mechanism for determining the accuracy of a temperature sensor involves controlling the ambient temperature of the device while taking measurements with the sensor. Any difference between the ambient temperature and the measured temperature reflect variances in the sensor's accuracy. Once identified, these discrepancies in the sensor's accuracy can be accounted for by trimming the sensor. In this method, the ambient temperature may be controlled by either controlling the air surrounding the device to a desired temperature or by dipping the device into a thermal fluid bath set at the desired temperature. Both of these approaches require specialized hardware that is expensive to purchase, operate and maintain.
In certain scenarios, the accuracy of the testing measurements themselves may be uncertain. For instance, where forced air is used, such as an oven, maintaining a stable temperature is complicated due to temperature gradients that can form within the controlled environment in which the test is being conducted. Such gradients can be partially eliminated by circulating the forced air that is used, but this itself introduces uncertainty to the highly precise testing measurements made using the sensor.
Another disadvantage of this first mechanism is the time required for each individual measurement. Before any measurements can be made with the sensor, this method requires the device to settle to the desired temperature. This settling time can be very slow depending on several factors such as the starting die temperature, the different packaging that may be used with the sensor and the different handling and testing equipment that may be used in this process. The different settling characteristics of thermal fluid versus forced air flow may add further uncertainty that may often be resolved by extending the settling time.
A second mechanism for determining the accuracy of a temperature sensor involves simulating its use. A set of thermal voltages is obtained by forcing a series of discrete currents as inputs to the diodes or other thermal voltage generating component of the temperature sensor. The generated thermal voltage information can then be used to calculate the die temperature. Since this method simulates use of the sensor in a test environment using a sensor that has not yet been trimmed, numerous sources of measurement error are possible. Additionally, this method requires highly calibrated external current sources capable of reliable precision. Numerous disadvantages and a more detailed description of this conventional method are provided below.
A need is present for a mechanism by which the accuracy of temperature sensor can be determined without relying on methods that require controlling ambient temperatures while also avoiding certain of the numerous disadvantage of using conventional simulated forced-current measurements.